1. Technical Field
The present invention relates to micro particles for use in clinical measurements and a process for producing such particles.
2. Description of the Prior Art
In clinical testing by immunochemical techniques, micro particles are used as carriers for determining materials present in trace amounts in boby fluids, such as IgA, IgD, IgE and IgG. Typically, the micro particles used are biological particles such as red corpuscles. These particles are sensitized with an antigen or antibody, which reacts with the antibody or antigen in the sample to cause either hemagglutination or hemagglutination inhibition for determination of the the antibody or antigen present in the sample in a trace amount. Instead of biological carriers, non-biological carriers have recently been used, for example, micro particles of synthetic latices or minerals such as bentonite and rock crystal. For example, in pregnancy diagnosis involving the detection of the human placental gonadotropic hormone in the urine and body fluids of the subject, a latex having anti-HCG adsorbed physically on the surface is mixed with a sample (e.g. serum) to check for the presence of latex aggregation.
Most of the solid micro particles used as carriers in clinical immunochemical assay have no particular bound functional groups on their surface, and the binding of the carrier to an antigen or antibody is simply a physical binding that depends on the adsorption of the antigen or antibody. Therefore, the binding force is weak and frequent dissociation of the antibody-antigen bonding has caused an error in the determination of the target material.
The latices of the conventional non-biological particles most commonly used are in most cases produced by emulsion polymerization using a catalyst in the polymerization system containing low concentrations of a monomer and high concentrations of an emulsifier. The resulting particles have a relatively wide size distribution ranging from 0.01 to 2 microns, with a high incidence of particles smaller than 1 micron. For ordinary immunochemical determination, carrier particles with a size of about 2 to 3 microns are preferred. However, synthesis of micro particles of a 2 or 3 micron size by emulsion polymerization involves several problems such as prolonged reaction time and the need for special process conditions. On the other hand, catalytic polymerization is disadvantageous in that impurities such as catalysts are introduced into the resulting particles to impair their physical properties. But in all likelihood, the swollen latex particles are not necessarily in a spherical form and may have different properties than the latex particles produced by direct polymerization.